Impeding effect of the Al3(Er,Zr,Li) particles on planar slip and intergranular fracture mechanism of Al-3Li-1Cu-0.1Zr-X alloys

The microstructure and mechanical properties of Al-3Li-1Cu-0.1Zr-xEr (x = 0, 0.1) alloys were investigated. With an addition of 0.1 wt% Er, dispersive core-shell structure Al3(Er,Zr,Li) particles were presented and the recrystallization was restrained. Besides, the trace of dislocations bypassing the Al3(Er,Zr,Li) particles was observed. Herein, the Orowan mechanism was also verified as the main strengthening mechanism of the Al3(Er,Zr,Li) particles by comparing the theoretical value in different strengthening mechanisms with the yield strength. The result demonstrated the impeding effect of the Al3(Er,Zr,Li) particles on the planar slip induced by shearing of the Al3Li, which also corresponded to the disappearance of the plastic instability in the alloy with Er addition. The Al-3Li-1Cu-0.1Zr-0.1Er alloy aged for 56 h possessed better ultimate tensile strength of 306 MPa and yield strength of 235 MPa. Interestingly, this alloy with unremarkable planar slip manifested lower elongation of 9.4% and obvious intergranular fracture when compared to the alloy without Er. To study this specific phenomenon, the hardness of grain interior and grain boundaries was investigated. The result showed that the intergranular fracture of this alloy was induced by higher strength of the grain interior than that of the grain boundaries, while the effect of the traditional planar slip mechanism was not apparent.